Wafer transfer systems are used to provide an automated transfer of semiconductor wafers from one position to another position. For example, the wafers contained in a cassette may be moved individually to a processing chamber for depositing and patterning layers of material for forming integrated circuit chips. Robotic handling devices are preferred, since human handling is more likely to cause contamination.
Conventional cassettes include slots that support the wafers in a vertical orientation. The wafers are removed from a cassette by lifting the wafers through an open top portion of the cassette. An automated transfer system that may be used to move semiconductor wafers between a cassette and a processing chamber is described in U.S. Pat. No. 4,449,885 to Hertel et al. The transfer system of Hertel et al. includes a cassette conveyor assembly for moving one or more cassettes horizontally. An elevator blade passes upwardly through the cassette to contact a lower edge of a wafer that has been moved into place by the conveyor assembly. The wafer is then raised to a position in which the elevator blade transfers the wafer to a vacuum chuck of a processing chamber. When the processing of the wafer has been completed, the wafer is returned to the cassette by the elevator blade.
Another type of wafer storage device is referred to as a Standardized Mechanical InterFace (SMIF) pod. A SMIF pod is described in U.S. Pat. No. 5,653,565 to Bonora et al. The wafers are held in a horizontal orientation, rather than a vertical orientation. The Bonora et al. patent describes a typical SMIF system as having three main components: (1) a sealed pod for storing and transporting cassettes that hold the semiconductor wafers; (2) enclosures placed over the cassette ports and wafer processing areas of processing equipment, so that the environments within the pods and the enclosures become miniature clean spaces; and (3) a transfer mechanism to load and unload wafers from the sealed pod without contamination of the wafers. In operation, when the semiconductor wafers are being transferred into the processing equipment, the pod is loaded onto an access port along an upper horizontal surface of the processing equipment. The pod door and the access port are preferably opened simultaneously, so that the exposure of the wafers to particles is minimized. An elevator lowers the pod door and the door of the access port, with the cassette riding on the pod door into the processing chamber. Thus, the wafers are removed from the pod in a protected manner.
Another type of wafer container is described in U.S. Pat. No. 5,711,427 to Nyseth. The Nyseth wafer container is described for use with 300 mm diameter semiconductor wafers. The container is sometimes referred to in the industry as a Front Opening Unified Pod (FOUP), since the wafers are stored in a horizontal orientation and the access door to the pod is located on a side that is perpendicular to the horizontally stored wafers. Automated transfer systems for use with FOUPs have been designed. The transfer systems are significantly different than the systems used with other types of containers, since the door is vertically mounted and the wafers are horizontally stored.
Typically, the access door of the FOUP includes a latching mechanism to ensure that the door remains in place until removal or insertion of wafers into the pod is desired. Devices for automatically removing the access door are known. Such devices typically rest on the floor adjacent to the equipment on which the FOUP is rested. A mechanism rises along guide rails to the access door and unlatches the door. The mechanism is then lowered to a rest position. One concern with such a device is that it requires stand-alone automated equipment to accommodate the movement of the door-removal mechanism. This may be undesirable in some applications. Another concern is that the extended movement of the door-removal mechanism may promote the generation of particles, since motors or other drive devices must be used in the operation of the mechanism. This is undesirable in an environment in which semiconductor wafers are to be exposed.
What is needed is a system for manipulating an access door of a wafer-supporting device such that system real estate requirements and the risk of generating particles are low.